Microwave plasma process device, plasma ignition method, plasma forming method, and plasma process method

ABSTRACT

A microwave plasma processing apparatus is disclosed that enables fast and easy plasma ignition at the pressure for plasma processing In the microwave plasma processing apparatus, a plasma ignition facilitating unit is provided to facilitate plasma ignition induced by a microwave. The plasma ignition facilitating unit includes a deuterium lamp that emits vacuum ultraviolet rays, and a transmission window that allows the vacuum ultraviolet rays to penetrate and irradiate a plasma excitation space. The transmission window is a convex lens, and focuses the vacuum ultraviolet rays to enhance ionization of the plasma excitation gas. With such a configuration, it is possible to induce plasma ignition easily and quickly.

TECHNICAL FIELD

[0001] The present invention generally relates to a plasma processingapparatus, and particularly, to a plasma processing apparatus thatperforms plasma processing using plasma excited by a microwave.

BACKGROUND OF THE INVENTION

[0002] In recent years and continuing, among plasma processingapparatuses, the microwave plasma processing apparatus is attractingattention. Compared with other plasma processing apparatuses, such as aparallel plate plasma processing apparatus and an ECR plasma processingapparatus, the plasma potential is relatively low in the microwaveplasma processing apparatus, enabling generation of plasma having a lowelectron temperature and low ion energy.

[0003] Therefore, with the microwave plasma processing apparatus, it ispossible to prevent metal contamination and ion irradiation damage to asubstrate subjected to plasma processing. In addition, because a plasmaexcitation space can be separated from the plasma processing space, itis possible to carry out plasma processing independent of materials ofthe substrate and patterns formed on the substrate.

[0004] In the microwave plasma processing apparatus, a gas for excitingplasma (referred to “plasma excitation gas”) is fed into a chamberfirst, and then the microwave is introduced to the plasma excitation gasto start the generation of plasma (plasma ignition). Because of the highfrequency of the microwave, the electrical field of the microwavechanges before electrons of the plasma excitation gas are sufficientlyaccelerated, making plasma ignition difficult. Additionally, in recentplasma processing, a pressure of the plasma excitation gas as low as,for example, 67 Pa (about 0.5 Torr) is sometimes required. Because ofthe low pressure, the density of the plasma excitation gas is low,further making plasma ignition difficult.

[0005] In the microwave plasma processing apparatus, differing from theparallel plate plasma processing apparatus, the microwave is emittedfrom a microwave antenna, and there is no electrical field applied tothe substrate to be processed, therefore, free electron emission orother phenomena causing plasma ignition do not occur, making plasmaignition more difficult.

[0006] In the microwave plasma processing apparatus of the related art,usually, the pressure inside the processing chamber is set high at thetime of plasma ignition, for example, the pressure is set to 133 Pa(about 1 Torr) so as to induce plasma ignition easily; after theignition, the pressure is lowered to, for example, 7 Pa (about 50mTorr). However, in this plasma ignition, an additional controlprocedure not relevant to the object plasma processing has to be gonethrough to increase the pressure inside the processing chamber forplasma ignition and to lower the pressure after the plasma ignition, andthis lengthens the preparation time before plasma processing starts, andlowers throughput.

DISCLOSURE OF THE INVENTION

[0007] Accordingly, a general object of the present invention is toprovide a novel and useful microwave plasma processing apparatus, aplasma ignition method, a plasma forming method, and a plasma processingmethod able to solve one or more problems of the related art.

[0008] A more specific object of the present invention is to provide amicrowave plasma processing apparatus, a plasma ignition method, aplasma forming method, and a plasma processing method enabling fast andeasy plasma ignition at a pressure for plasma processing.

[0009] According to an aspect of the present invention, there isprovided a microwave plasma processing apparatus that generates plasmaby a microwave and carries out plasma processing, comprising a plasmaignition facilitating unit configured to facilitate plasma ignition bythe microwave.

[0010] According to another aspect of the present invention, there isprovided a method of inducing plasma ignition by a microwave, comprisingthe steps of: evacuating a processing chamber to a predetermined vacuum;supplying a plasma excitation gas to the processing chamber; emitting atleast one of vacuum ultraviolet rays, X-rays, a laser beam, an electronbeam, and light from an excimer lamp to the plasma excitation gas insidethe processing chamber; and introducing the microwave to the plasmaexcitation gas in the processing chamber to induce plasma ignition.

[0011] According to another aspect of the present invention, there isprovided a method of forming plasma by radiating a microwave from amicrowave antenna, comprising the steps of: evacuating a processingchamber to a predetermined vacuum; supplying a plasma excitation gas tothe processing chamber; emitting vacuum ultraviolet rays to the plasmaexcitation gas inside the processing chamber through a transmissionwindow mounted on the processing chamber; focusing, by the transmissionwindow, the vacuum ultraviolet rays to a predetermined position;ionizing at least a part of the plasma excitation gas; and radiating themicrowave into the processing chamber to induce plasma ignition.

[0012] According to another aspect of the present invention, there isprovided a plasma processing method for processing a substrate usingplasma formed by radiating a microwave from a microwave antenna,comprising the steps of: evacuating a processing chamber to apredetermined vacuum; supplying a plasma excitation gas to theprocessing chamber; emitting vacuum ultraviolet rays to the plasmaexcitation gas inside the processing chamber through a transmissionwindow mounted on the processing chamber; focusing, by the transmissionwindow, the vacuum ultraviolet rays to a predetermined position;ionizing at least part of the plasma excitation gas; radiating themicrowave into the processing chamber to induce plasma ignition; andfeeding a process gas for processing the substrate into the processingchamber after the plasma ignition.

[0013] According to the present invention, because a plasma ignitionfacilitating unit is provided to facilitate plasma ignition induced by amicrowave, it is possible to induce plasma ignition easily and quicklywith only the microwave, even under conditions not favorable to plasmaignition. The plasma ignition facilitating unit may have a configurationin which vacuum ultraviolet rays, x-rays, a laser beam, an electronbeam, or light from an excimer lamp is emitted to a plasma excitationspace to induce plasma ignition easily. Particularly, it is preferableto use vacuum ultraviolet rays emitted from a deuterium lamp, forexample, vacuum ultraviolet rays at a wavelength of 135 nm, to penetratea transmission window and irradiate the plasma excitation space in theprocessing chamber. The plasma excitation gas in the plasma excitationspace is ionized by the vacuum ultraviolet rays to serve as seeds forgenerating plasma. As a result,, by introducing a microwave, it ispossible to generate plasma easily.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a schematic view showing a configuration of a microwaveplasma processing apparatus according to an embodiment of the presentinvention;

[0015]FIG. 2 is a plan view showing the focusing position of thetransmission window relative to the semiconductor wafer;

[0016]FIG. 3 is a flowchart showing the plasma processing carried out bythe microwave plasma processing apparatus shown in FIG. 1;

[0017]FIG. 4 is a schematic view showing a configuration of amodification to the microwave plasma processing apparatus shown in FIG.1; and

[0018]FIG. 5 is a schematic view showing a configuration of anothermodification to the microwave plasma processing apparatus shown in FIG.1.

BEST MODE FOR CARRYING OUT THE INVENTION

[0019] Below, preferred embodiments of the present invention areexplained with reference to the accompanying drawings.

[0020]FIG. 1 is a schematic view showing a configuration of a microwaveplasma processing apparatus according to an embodiment of the presentinvention.

[0021] The microwave plasma processing apparatus 10 includes aprocessing chamber 12, a slot antenna (microwave antenna) 14 above theprocessing chamber 12, a dielectric separation wall 16 below the slotantenna 14, a plasma excitation gas shower plate 18 below the dielectricseparation wall 16 for feeding a plasma excitation gas, a process gasshower plate 20 below the plasma excitation gas shower plate 18 forfeeding a process gas, a stand 22 below the process gas shower plate 20,and a magnetron 24 for generating a microwave.

[0022] The microwave generated by the magnetron 24, for example, at 2.45GHz, is directed to the slot antenna 14 through a wave guide (notillustrated). The microwave directed to the slot antenna 14 passesthrough the dielectric separation wall 16 and the plasma excitation gasshower plate 18, and is directed to a plasma excitation space 26.

[0023] A plasma excitation gas, for example, any noble gas of Argon(Ar), Krypton (Kr), and Xenon (Xe), comes out from the plasma excitationgas shower plate 18 and enters the plasma excitation space 26, where theplasma excitation gas is excited by the microwave and plasma isgenerated. The plasma generated in the plasma excitation space 26, forexample, passes through openings arranged in a lattice manner in theprocess gas shower plate 20, and is fed to a processing space 28.

[0024] From the process gas shower plate 20, a process gas is suppliedto the processing space 28. On the stand 22 disposed in the processingspace 28, a semiconductor wafer W, such as a silicon wafer, is locatedto be subjected to plasma processing in the process gas and the plasma.The resulting gas of the plasma processing is exhausted by a notillustrated pump through an exhaust port 12 a provided at the bottom ofthe processing chamber 12.

[0025] Next, plasma ignition in the microwave plasma processingapparatus 10 is explained.

[0026] In the microwave plasma processing apparatus 10, plasma ignitionis induced by the introduced microwave in the plasma excitation space26. However, if the pressure inside the processing chamber 12 is low, itis difficult to induce plasma ignition with only a microwave. Therefore,in the microwave plasma processing apparatus 10 of the presentembodiment, a plasma ignition facilitating unit is provided to assist orfacilitate plasma ignition induced by the microwave.

[0027] The plasma ignition facilitating unit of the present embodimentincludes a deuterium lamp 30 mounted on a side wall of the processingchamber 12 that defines the plasma excitation space 26 and atransmission window 32. The deuterium lamp 30 emits vacuum ultravioletrays at a wavelength of 135 nm. The vacuum ultraviolet rays pass throughthe transmission window 32 and are directed to the plasma excitationspace 26, where the vacuum ultraviolet rays induce ionization of theplasma excitation gas, and thereby facilitate microwave plasma ignition.It is preferable that the transmission window 32 be made from CaF₂,MgF₂, LiF and so on so that the vacuum ultraviolet rays at shortwavelengths are not absorbed. In addition, because the vacuumultraviolet rays have a very good ionization efficiency at a pressurearound a range from 1.34 Pa (about 0.01 Torr) to 13.4 Pa (about 0.1Torr), it is preferable to use the vacuum ultraviolet rays in the plasmaignition facilitating unit in the present embodiment.

[0028] As described above, since the vacuum ultraviolet rays emittedfrom the deuterium lamp 30 have short wavelengths and thus high energy,they can efficiently ionize the plasma excitation gas constituted by anoble gas. For example, Krypton (Kr) gas can be used as the plasmaexcitation gas. The energy necessary to remove an electron from aKrypton atom is 13.8 eV. The energy of a photon of the vacuumultraviolet rays at a wavelength of 135 nm is 9 eV. Therefore, theKrypton atom receives 18 eV if two such photons are absorbed, making itpossible to remove an electron from the Krypton atom.

[0029] In other words, when the Krypton gas is irradiated by the vacuumultraviolet rays at a wavelength of 135 nm, a considerable number ofelectrons are emitted from the Krypton atoms, inducing ionization of theKrypton gas. If a microwave is introduced to the ionized Krypton gas, itis possible to easily induce plasma ignition.

[0030] Here, in order for a Krypton atom to absorb two photons, it isnecessary for the incident photons to continuously impact the Kryptonatoms, namely, transfer energy to the Krypton atoms continuously, andpreferably, the strength of the vacuum ultraviolet rays is high. Toincrease the strength of the vacuum ultraviolet rays, it is preferablethat the transmission window 32 be made into a convex lens to focus thevacuum ultraviolet rays to a specified position in the plasma excitationspace 26. Preferably, the focusing position (P) of the vacuumultraviolet rays is one of the positions where the electric field of themicrowave is strongest, for example, at nodes of a stationary wave ofthe microwave or middle points between two nodes (namely, antinodes ofthe stationary wave) in the plasma excitation space 26.

[0031] In the plasma ignition facilitating unit of the presentembodiment, the process gas shower plate 20 is made of conductivematerials, and the microwave is reflected by the plasma excitation gasshower plate 18 and the process gas shower plate 20, thereby, thestationary wave of the microwave is to generated between the plasmaexcitation gas shower plate 18 and the process gas shower plate 20.Therefore, in the present embodiment, a convex lens is selected to beused as the transmission window 32 so that its focal point is located atan antinode of the stationary wave. Namely, the distance L from theplasma excitation gas shower plate 18 to the focal point equals toone-fourth of the wave length λ of the microwave (λ/4).

[0032] Consequently, because the high strength vacuum ultraviolet raysfocused by the transmission window 32 irradiate a portion of the plasmaexcitation space 26 where ionization most probably occurs, absorption oftwo photons by a Krypton atom becomes easy, and this further facilitatesplasma ignition. It should be noted that the distance L mentioned aboveis not limited to one-fourth of the wave length A of the microwave, butit may be other distances corresponding to other positions of theantinodes of the stationary wave, for example, 3λ/4, 5λ/4, or nλ/4(where n is an integer).

[0033]FIG. 2 is a plan view of the plasma excitation space 26 when thesemiconductor wafer W is viewed from the top perpendicularly, showingthe focusing position of the transmission window 32. Preferably, theposition (P) where the vacuum ultraviolet rays are focused, namely, theposition of the focusing point of the transmission window 32 (a convexlens), is out of the right cylindrical region with the semiconductorwafer W as a base. Specifically, if the plasma ignition takes placeabove but close to the semiconductor wafer W, it may result in adverseinfluence on the semiconductor wafer W because the semiconductor wafer Wends up being on the path for propagating the plasma excitation gas. Inorder to avoid this, it is preferable that the position of the plasmaignition be out of the right cylindrical region with the semiconductorwafer W as a base. In FIG. 2, the process gas shower plate 20 is notillustrated.

[0034]FIG. 3 is a flowchart showing the plasma processing carried out bythe microwave plasma processing apparatus 10 of the present embodiment.

[0035] As described above, in the microwave plasma processing apparatus10 of the present embodiment, first, the processing chamber 12 isevacuated to a predetermined vacuum (step 1). Then, a plasma excitationgas is supplied to the plasma excitation space 26 (step 2). After that,the deuterium lamp 30 emits vacuum ultraviolet rays, and the vacuumultraviolet rays pass through the transmission window 32 and aredirected to the plasma excitation space 26 (step 3). The vacuumultraviolet rays remove electrons from atoms of the plasma excitationgas, and in this state, a microwave is introduced to the plasmaexcitation space 26 from the slot antenna 14 to induce plasma ignition(step 4). When plasma ignition is induced, plasma is generatedcontinuously from then on. The thus generated plasma passes through theopenings in the process gas shower plate 20, and enters the processingspace 28. With the process gas and the plasma, plasma processing iscarried out on the semiconductor wafer W (step 5).

[0036] For example, in the case of forming one of a silicon dioxidefilm, a silicon nitride film, and a silicon nitride oxide film on asilicon wafer, at least one of O₂, NH₃, N₂, and H₂ may be used as theprocess gas and supplied to the processing space 28 from the process gasshower plate 20. In the case of etching a silicon wafer, for example,fluorocarbon or halogen gas may be used as the process gas and suppliedto the processing space 28 from the process gas shower plate 20.

[0037] Here, the process gas is supplied from the process gas showerplate 20 to the processing space 28, which is separated from the plasmaexcitation space 26, and flows from the wafer W toward the exhaust port12 a provided at the bottom of the processing chamber 12. That is, theprocess gas cannot enter into the plasma excitation space 26. Therefore,at the time of plasma ignition, the process gas does not exist in theplasma excitation space 26, and this prevents problems caused bydissociation of the process gas at the time of plasma ignition.

[0038] While the invention has been described with reference topreferred embodiments, the invention is not limited to theseembodiments, but numerous modifications could be made thereto withoutdeparting from the basic concept and scope described in the claims.

[0039] For example, it is described above that the deuterium lamp 30 andthe transmission window 32 are mounted on the side wall of theprocessing chamber 12, but they can also be mounted at differentpositions.

[0040]FIG. 4 is a schematic view showing a configuration of amodification to the microwave plasma processing apparatus shown in FIG.1.

[0041] In the microwave plasma processing apparatus 10A shown in FIG. 4,the deuterium lamp 30 and the transmission window 32 are mounted on thebottom of the processing chamber 12. In this case, because the wallsdefining the plasma excitation space 26 are smooth, it is possible toprevent abnormal microwave discharge caused by a discontinuity of thewalls defining the plasma excitation space 26.

[0042]FIG. 5 is a schematic view showing a configuration of anothermodification to the microwave plasma processing apparatus shown in FIG.1.

[0043] As shown in FIG. 5, the deuterium lamp 30 is mounted on the outerside of the processing chamber 12, and the space between the deuteriumlamp 30 and the transmission window 32 (the space that the vacuumultraviolet rays pass through) is maintained to be in a vacuum, becauseotherwise the 135 nm vacuum ultraviolet rays emitted from the deuteriumlamp 30 are absorbed in the air. Alternatively, the space between thedeuterium lamp 30 and the transmission window 32 may be filled with ahelium gas.

[0044] In addition, the deuterium lamp 30 may have a reflector tocondense the vacuum ultraviolet rays emitted from the deuterium lamp 30in various directions. In this case, it is not necessary to make thetransmission window 32 a convex lens; for example, a planar transmissionwindow 32 is sufficient.

[0045] Further, it is described above that the plasma ignitionfacilitating unit is configured to emit the vacuum ultraviolet rays, butthe present invention is not limited to this. The present invention isapplicable to any other configuration provided that ionization of theplasma excitation gas is enabled. For example, instead of the vacuumultraviolet rays, X-rays, a laser beam, an electron beam, or light froman excimer lamp may be used to ionize the plasma excitation gas.

[0046] Industrial Applicability

[0047] According to the present invention, because a plasma ignitionfacilitating unit is provided to facilitate plasma ignition induced by amicrowave, it is possible to induce plasma ignition easily and quicklywith the microwave only, even under conditions not favorable to plasmaignition. The plasma ignition facilitating unit may have a configurationin which the vacuum ultraviolet rays from a deuterium lamp penetrate atransmission window and irradiate a plasma excitation space in aprocessing chamber; thereby, it is possible to facilitate plasmaignition with a simple configuration.

1. A microwave plasma processing apparatus that generates plasma by amicrowave and carries out plasma processing, comprising: a plasmaignition facilitating unit configured to facilitate plasma ignition bythe microwave.
 2. The microwave plasma processing apparatus according toclaim 1, wherein the microwave used for generation of the plasma isdirected into a processing chamber from a microwave antenna through amicrowave transmission window that is a part of the processing chamber.3. The microwave plasma processing apparatus according to claim 1,wherein the plasma ignition facilitating unit emits at least one ofvacuum ultraviolet rays, X-rays, a laser beam, an electron beam, andlight from an excimer lamp to a plasma excitation space to induce theplasma ignition.
 4. The microwave plasma processing apparatus accordingto claim 3, wherein the plasma ignition facilitating unit comprises: adeuterium lamp that emits the vacuum ultraviolet rays; and atransmission window that directs the vacuum ultraviolet rays passingtherethrough to the plasma excitation space.
 5. The microwave plasmaprocessing apparatus according to claim 4, wherein a space between thedeuterium lamp and the transmission window is maintained to be at avacuum.
 6. The microwave plasma processing apparatus according to claim4, wherein a space between the deuterium lamp and the transmissionwindow is filled with a helium gas.
 7. The microwave plasma processingapparatus according to claim 4, wherein the deuterium lamp and thetransmission window are mounted on side walls of a processing chamberdefining the plasma excitation space.
 8. The microwave plasma processingapparatus according to claim 4, wherein the deuterium lamp and thetransmission window are mounted on a bottom of a processing chamberdefining the plasma excitation space.
 9. The microwave plasma processingapparatus according to claim 4, wherein the transmission window includesa convex lens having a focal point at a predetermined position in theplasma excitation space.
 10. The microwave plasma processing apparatusaccording to claim 9, wherein the predetermined position is out of aspace right above a substrate to be processed.
 11. The microwave plasmaprocessing apparatus according to claim 9, wherein at the predeterminedposition, an electric field of the microwave radiated inside theprocessing chamber is a maximum.
 12. The microwave plasma processingapparatus according to claim 9, wherein a distance from thepredetermined position to a surface of a plasma excitation gas showerplate for feeding the plasma excitation gas into the plasma excitationspace is a multiple of λ/4, where λ is the wave length of the microwave.13. The microwave plasma processing apparatus according to claim 4,wherein the transmission window is formed from one of CaF₂, MgF₂, andLiF.
 14. The microwave plasma processing apparatus according to claim 3,wherein the plasma excitation space is separated from a processing spaceby a process gas shower plate, and a process gas is supplied from theprocess gas shower plate to the processing space thereby preventing theprocess gas from entering into the plasma excitation space.
 15. A methodof inducing plasma ignition by a microwave, comprising the steps of:evacuating a processing chamber to a predetermined vacuum; supplying aplasma excitation gas to the processing chamber; emitting at least oneof vacuum ultraviolet rays, X-rays, a laser beam, an electron beam, andlight from an excimer lamp to the plasma excitation gas inside theprocessing chamber; and introducing the microwave to the plasmaexcitation gas in the processing chamber to induce plasma ignition. 16.A method of forming plasma by radiating a microwave from a microwaveantenna, comprising the steps of: evacuating a processing chamber to apredetermined vacuum; supplying a plasma excitation gas to theprocessing chamber; emitting vacuum ultraviolet rays to the plasmaexcitation gas inside the processing chamber through a transmissionwindow mounted on the processing chamber; focusing, by the transmissionwindow, the vacuum ultraviolet rays to a predetermined position;ionizing at least a part of the plasma excitation gas; radiating themicrowave into the processing chamber to induce plasma ignition.
 17. Aplasma processing method for processing a substrate using plasma formedby radiating a microwave from a microwave antenna, comprising the stepsof: evacuating a processing chamber to a predetermined vacuum; supplyinga plasma excitation gas to the evacuated processing chamber; emittingvacuum ultraviolet rays to the plasma excitation gas inside theprocessing chamber through a transmission window mounted on theprocessing chamber; focusing, by the transmission window, the vacuumultraviolet rays to a predetermined position; ionizing at least a partof the plasma excitation gas; radiating the microwave into theprocessing chamber to induce plasma ignition; and feeding a process gasfor processing the substrate into the processing chamber after theplasma ignition.
 18. The plasma processing method according to claim 17,wherein the plasma excitation gas comprises a noble gas including one ofArgon (Ar), Krypton (Kr), and Xenon (Xe).
 19. The plasma processingmethod according to claim 17, wherein the process gas includes at leastone of O₂, NH₃, N₂, and H₂.
 20. The plasma processing method accordingto claim 19, wherein the substrate is a silicon wafer, and the processgas is fed into the processing space to form at least one of a silicondioxide film, a silicon nitride film, and a silicon nitride oxide filmon the silicon wafer.
 21. The plasma processing method according toclaim 17, wherein the process gas includes at least one of afluorocarbon gas and a halogen gas.
 22. The plasma processing methodaccording to claim 21, wherein the process gas is fed into theprocessing space to etch the substrate.
 23. The plasma processing methodaccording to claim,17, wherein the plasma excitation gas is supplied toa plasma excitation space separated from a processing space in which thesubstrate is located, and the process gas is supplied to the processingspace thereby preventing the process gas from entering into the plasmaexcitation space at the time of plasma ignition.